1. Field of the Invention
The present invention relates, in general, to toothbrushes and methods of producing the same and, more particularly, to a toothbrush in which a pressure relief unit is installed in a head part of the toothbrush, and a method of producing the same.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Generally, to produce a toothbrush, first, a toothbrush body having holes in a head part thereof is manufactured. Subsequently, bristles, folded in half, are set in the holes of the head part. The bristles are fastened to the toothbrush body by inserting wires, which are made of elastic metal and have a length greater than the diameter of the hole, into the holes.
However, such a toothbrush production method has disadvantages in that, because bristles are not reliably fixed to the toothbrush body, the bristles are easily removed from the toothbrush body, and impurities are easily held in the holes formed in the head part of the toothbrush. As well, this toothbrush producing method is problematic in that bristles cannot be set in various patterns.
As an example of techniques to overcome the above-mentioned problems, in Korean Patent No. 360977, bristles are set in a mold of an injection molding machine having a bristle setting device. Thereafter, portions of the bristles protruding into the mold are thermally welded through a heat treatment process. Subsequently, a toothbrush body is injection-molded along with the bristles so that the bristles are integrated with the toothbrush body. In this technique, the bristles are reliably fixed to the toothbrush body. Furthermore, because it is not necessary to form holes in a head part of the toothbrush, the problems of the prior art are solved.
However, the above-mentioned conventional technique has disadvantages as follow.
First, because toothbrushes are manufactured using a mold having a constant shape, it is very difficult to change the shape of the toothbrush body. The toothbrush body is frequently subject to changes due to trends. Therefore, the difficulty in changing the shape of the toothbrush body is a serious problem. Of course, toothbrush bodies having different shapes may be simultaneously manufactured by mounting several different molds to a single injection molding machine. However, in this case, there is a problem in that the same number of different toothbrushes must be manufactured and marketed.
Second, there is a problem in that if an error occurs even in one process of a series of manufacturing processes, all other processes must also be stopped. That is, the conventional technique consists of processes as follow: (1) a process of setting bristles in the mold, (2) a process of thermally welding parts of the bristles which protrude into the mold, and (3) a process of injection-molding a toothbrush. If an error occurs in even one among the above-mentioned processes, the production must be stopped.
Third, the injection molding machine is not operated during the setting and thermal welding processes. Accordingly, in consideration of the expensive injection molding machine having the bristle setting device, productivity per hour is markedly reduced.
To solve the above-mentioned problems, another technique was proposed in Korean Patent Application No. 10-2003-0036887.
In this technique, bristles are set in through holes formed through a head insert 10, which is made of plastic and has a thickness ranging from 1.5 to 3.0 mm, such that parts of the bristles protrude from a back surface of the head insert 10 by 1 to 3 mm. Thereafter, the protruded parts of the bristles are thermally welded, thus separately manufacturing the head insert 10 which has the bristles and is a partial-product. Subsequently, the head insert 10 having the bristles is placed in a cavity of the mold such that the bristles are placed outside the cavity of the mold. Thereafter, a toothbrush body is injection-molded by injecting resin into the mold using a normal injection molding machine, thus producing a toothbrush.
In this technique, a process of setting the bristles in the head insert 10, a process of thermally welding parts of the bristles which protrude from the back surface of the head insert 10, and a process of placing the head insert 10 having the bristles in the mold and injection-molding a toothbrush body are separately conducted. Therefore, even if an error occurs in one process, other processes can be conducted. Therefore, the rate of operation of equipment is markedly enhanced. Furthermore, the shape of the toothbrush can be easily changed merely by manufacturing an additional mold for the injection molding machine, which is relatively inexpensive.
However, in this technique, when injection-molding the toothbrush body after the head insert 10 having the bristles is placed in the mold, a phenomenon, in which resin may flow out along the bristles due to injection pressure, frequently arises. As such, if resin flows out along the bristles, the bristles become bonded to each other, so the value of the product is deteriorated.
Meanwhile, another toothbrush manufacturing method, in which a head insert 10 having bristles is separately manufactured and is then bonded to a toothbrush body, manufactured through a separate process, using ultrasonic waves, was proposed. In this technique, because a process of manufacturing the head insert 10 and a process of manufacturing the toothbrush body are separately conducted, the problem of deterioration of workability is solved. However, in this technique, because the head insert 10 is inserted into a head part of the toothbrush body and integrated with the toothbrush body using an ultrasonic bonding method, the head insert 10 must be precisely aligned with the toothbrush body. Therefore, an accurate mold is required, thus the price of equipment is excessively increased. Furthermore, there is a problem in that the head part of the toothbrush becomes too thick.
Generally, a head part of a toothbrush that is thin and narrow is more convenient for a user and increases tooth brushing efficiency. However, in the above-mentioned technique, because the head insert is bonded to the head part of the toothbrush along a bonding line (b) defined on a sidewall of the head part, the head part of the toothbrush becomes relatively thick (see, FIG. 1). To reduce the thickness of the head part of the toothbrush, the bonding operation may be conducted on the front surface of the head part. However, this bonding method requires an increase in the area of the head part and may cause damage to the bristles. Therefore, this bonding method should not be conducted.